kim mulvahill joining us. and we are hearing this radioactive steam, if it is contained, could be released for weeks or even months? >> you know, that's the concern. and as you mentioned, the situation is evolving. now, as a precaution, nearly 200,000 people have been evacuated from a 12-mile radius around the crippled plant. 190 individuals have already been exposed to some radiation. and several workers have fallen ill with acute radiation sickness. many wonder what's the risk to the general public? when it comes to radiation exposure, scientists say there is a simple rule. no amount of exposure is safe. >> well, radiation is damaging the dna, which is the basic genetics of how cells divide in our body. >> reporter: and that damage can lead to cancer, which radiation expert dr. david brenner is the biggest concern. >> the bigger the risk the bigger the risk. the smaller the dose the smaller the risk. it doesn't happen overnight. 10, 20, 30 years after the exposure is when the cancer can appear. >> reporter: